It is well known in the field of medical electrical leads that proper coupling of stimulating electrodes to the right atrial wall is problematic, especially in respect of single pass DDD leads.
Over the years various attempts have been made to solve this problem by providing, for example, leads having positive affixation devices attached at or near the distal ends thereof such as screws, barbs and hooks, or by forming pre-formed J shapes or other configurations in the atrial portions of such leads.
See, for example, U.S. Pat. No. 4,154,247 to O'Neil for "Formable cardiac pacer lead and method of assembly and attachment to a body organ", U.S. Pat. No. 4,401,126 to Reenstierna for "Endocardial implantable lead for pacemaker" and U.S. Pat. No. 4,627,439 to Harris for "Prebent ventricular/atrial cardiac pacing lead", all of which are hereby incorporated by reference herein, each in its respective entirety. The foregoing patents all disclose single pass DDD leads having preshaped portions configured to cause the atrial electrode(s) thereof to appropriately contact and stimulate the right atrial wall.
While the leads disclosed in the foregoing patents solve some of the problems existing in the prior art respecting appropriate atrial electrode coupling in single pass leads, they produce no solution to the overriding problem, which is to provide a lead capable of providing good atrial coupling along the right atrial wall in a variety of heart shapes and sizes.
In addition to the problem of pre-formed single pass DDD leads not providing adequate electrode coupling under a variety of different physiologic conditions, there also exists the problem of implanting more than one lead in a human heart when reliable pacing of both the right atrium and right ventricle is to be carried out. In such a situation separate leads are typically implanted in the right atrium and in the right ventricle. Implanting two leads in a patient presents a challenge to the implanting physician because inserting two leads into the heart via the superior vena cava increases the surgical difficulty of the implantation procedure. Thus, while separate leads generally provide superior electrode coupling, they also present certain difficulties to the implanting physician.
The foregoing problems assume increased emphasis today owing to recent developments in heart failure treatment via pacing techniques. Effective, reliable pacing of the right atrium now assumes increased importance when treating heart failure.
Optimally pacing in heart failure includes pacing of four chambers of the heart. At a minimum, it is desirable to stimulate the left side of the heart via the intravenous route extending from the right side of the heart where synchronization of the cardiac cycle takes place via sensing of right atrial signals.
Thus, there exists a need to provide a medical electrical lead capable of solving the foregoing problems.